1. Field of the Invention
The present invention relates to a detecting system and, more particularly, to a system for detecting poor video editing.
2. Description of Related Art
For the limited broadcast bandwidth, current TV broadcasting typically uses alternate odd/even fields. As shown in FIG. 1, odd fields 10 and 12 have only odd-line video data, and even fields 11 and 13 have only even-line video data. New generation of TVs requires a higher vertical resolution, and accordingly a line doubler is used in a TV to perform a double frequency processing in order to increase the vertical resolution. The simplest double frequency processing is to directly merge adjacent odd and even fields to thereby form a progressive scan frame. However, because of a time difference between the adjacent odd and even fields, such a processing presents a sawtooth to a motion image.
To overcome the aforementioned problem, a line doubler preferably is equipped with a frame motion detector to detect a motion image. In addition, the line doubler can perform an inter-field interpolation of de-interlacing process on a still image and an intra-field interpolation of de-interlacing process on the motion image.
Another double frequency processing is achieved by determining if an image originates from a film. It is known that a film is formed by recording 24 frames per second. Accordingly, for displaying a film signal on an NTSC TV, it converts the 24 frames into 60 fields per second. As shown in FIG. 2, such a conversion is typically referred to as a “3:2 pull down”, i.e., two temporally successive film frames are converted into three fields and two fields respectively. For example, frame 14 is converted into field 18 (odd field), field 19 (even field) and field 20 (odd field), frame 15 is converted into field 21 (even field) and field 22 (odd field), and so on. Thus, upon such a double frequency processing, a perfect double frequency output can be obtained by combining all odd and even fields that correspond to the same frame when an image is determined to originate from a film signal. In this case, an image has no sawtooth and a motion image can have the highest vertical resolution.
For detecting an image source, frame or field motion data is used to determine whether the image source is a film signal or not. FIG. 3 shows an example of using frame motion detectors 31 to provide the required frame motion data. As shown in FIG. 3, each frame motion detector 31 can detect two successive odd or even fields to thereby output ‘1’ when the two successive odd or even fields are the same and ‘0’ when different. Accordingly, if a TV image is a segment of still frames, whether the image source is a film signal or not, the frame motion detector 31 outputs a sequence ‘11111, 11111, . . . ’. If the TV image is a segment of motion video signal, the frame motion detector 31 outputs a sequence ‘00000, 00000, . . . ’. If the TV image is a segment of motion film signal, the frame motion detector 31 outputs a sequence ‘10000, 10000, . . . ’.
The output of the frame motion detector 31 is applied to FIG. 4 in which a film detection state transition diagram is shown, thereby determining if an input image is of a 3:2 pull down film. States 0-5 of the film detection state transition diagram are video mode states, and states 6-10 are film mode states. As shown in FIG. 4, the diagram starts at state 0. For every input with ‘10000’, the state transition has to pass through state 4, which causes an increase on the counter 41. When the counter 41 exceeds a threshold, a state transition from state 4 to state 6 is performed, i.e., a TV image (video) mode state is changed into a film mode state.
As cited above, when an input image is of the 3:2 pull down film, the frame motion detector outputs ‘10000’ or ‘1111’. When the frame motion detector outputs a certain amount of ‘10000’, the film detection state transition diagram is changed from a video mode state to a film mode state and remains at the film mode state as long as the input is met with ‘1XXXX’.
The aforementioned technique can effectively detect whether an image originates from a film signal or not, and have a perfect double frequency output. However, it also causes the poor film editing, which impairs the 3:2 pull down proportion and outputs the image with a sawtooth. As shown in FIG. 5, fields 1-8 are from a film segment A, and fields 9-16 are from another film segment B. Due to a bad editing in the film segment B, field 9 and the following fields are not consistent with the 3:2 pull down process. Please refer again to FIG. 4 and the state transition diagram can only determine that the image is fit to the film mode at field 11. Therefore, when the field 9 is used as a basis to generate the television image, the field 9 and the field 10 originally from different film frames are combined into one image frame, and the television image incurs sawtooth effect as a result.
To overcome the aforementioned problem, U.S. Pat. No. 6,201,577 granted to Peter D. Swartz for a “Film source video detection” discloses a method for detecting a poor editing. The method detects the poor editing on a current output image and informs a film pattern detector to leave the film mode to thereby avoid combining two fields, which are not of a same frame, into a frame. However, such a detection is operated on the current output image, which cannot totally avoid an image from presenting a sawtooth because a line doubler outputs a frame with a sawtooth before a poor editing is detected. In addition, the prior art cannot leave the film mode in states 7-10 and thus possibly combines two fields of different frames into a frame, resulting in likely presenting a sawtooth to a TV image.
Therefore, it is desirable to provide an improved system for detecting poor video editing to mitigate and/or obviate the aforementioned problems.